The invention relates to limiting the presence and transmission of volatile components into the airspace of an insulating glass assembly.
Insulating glass assemblies such as insulating glass (IG) units and insulating sash assemblies often include a pair of glass panes maintained in a fixed spaced relation to each other by a spacing structure and sealing composition(s) that extend around the periphery of the inner facing surfaces of the glass sheets to define a sealed and insulating space between the glass panes. In the case of insulating sash assemblies, the spacing structure is an integral part of the sash frame and the glass panes are attached to the spacing structure by a sealant or adhesive composition. The sealant or adhesive composition is also used to seal the edges of the insulating glass assembly so as to establish a barrier that prevents moisture from penetrating into the interior of the assembly and potentially to prevent thermal property improvement gases, like argon, from leaving the airspace.
Insulating glass assemblies also include a desiccant disposed in the spacing structure. The desiccant can be in various forms including loose particles, powders and desiccant matrix compositions. Desiccant matrix compositions include a polymer matrix (i.e., carrier) and adsorbent disposed in the matrix. The adsorbents are capable of adsorbing moisture, volatile organic compounds, other volatile chemicals or combinations thereof.
The desiccant functions to remove moisture, and potentially chemical volatiles, from the sealed chamber of the insulating glass assembly, which if not removed can contribute to the visual appearance of chemical condensation on the glass surfaces, which is known as chemical fogging. Fog can form from moisture and volatile organic compounds present in the sealed chamber when the insulating glass assembly is manufactured, as well as volatile organic compounds emitted by various polymeric components of an insulating glass assembly.
Spacing structures traditionally have been in the form of a U-shaped metal channel. Recently polymeric spacing structures have been described for use in the construction of insulating glass assemblies. Polymeric spacing structures provide benefits in terms of the heat transmission performance of the assembly, one measure of which is referred to as the “U Factor” by those in the window industry. Polymeric spacing structures made from polyvinyl chloride have exhibited off-gassing of organic components when incorporated in insulating glass units. Polyvinyl chloride is also known to be moisture vapor permeable. It has been difficult to achieve acceptable performance from insulating glass assemblies that include a polymeric spacing structure using existing desiccant matrix compositions
Vapor barriers in the form of metal foils, electrostatic powder coatings, and chemical vapor deposition have been suggested for use on polyvinyl chloride spacing structures to prevent vapor from transmitting through the spacing structure and into the sealed airspace of the insulating glass assembly. However, applying such vapor barriers requires additional processing steps. In addition, the presence of a metal component such as a metal vapor barrier reduces the U Factor of the assembly.